Global System for Mobile Communications (GSM) is a widely used mobile system standard. FIG. 1 is a block diagram illustrating the architecture of a typical GSM system. In system 100, a Mobile Station (MS) 102 such as a handset communicates with a Base Transceiver Station (BTS) 104, which typically includes a tower or other structure with one or more antennas and associated radio transceivers. The BTS typically relays data between the mobile station and the core mobile network 108 via a dedicated point-to-point communication link to a Base Station Controller (BSC) 106. More than one BTS may be configured to communicate with the same BSC. Interface 110 between the BTS and the BSC is a synchronized interface. Requirements for the interface are specified by the GSM standard. The physical layer of the interface is typically implemented using a T1 or E1 link to provide a reliable connection between the BTS and the BSC. While the link is active, synchronization data is transferred at a rate specified by the network layer protocol. Interface 112 between the BTS and the MS is also a synchronized link with certain specifications defined by the GSM standard. Since the interface is wireless, it is sometimes referred to as an Air interface.
New generations of GSM architecture have been proposed to support more flexible network configurations and provide better voice and data services. It would be desirable to have GSM systems capable of communicating over the Internet and supporting network layer protocols such as the Internet Protocol (IP). It would also be useful for the new generations of GSM systems to be compatible with existing BSCs and MSs.